In the production of natural gas, such gas can be condensed into an easily transportable liquid natural gas (LNG) via a propane-precooled multicomponent-refrigerant (MCR) process. In such a process, the natural gas is cooled by multiple levels of, first, propane refrigeration, followed by the MCR refrigeration. The product is liquid natural gas at atmospheric pressure and a temperature of -260.degree. F.
The MCR is composed of nitrogen, methane, ethane and propane. These four components are gathered from various sources. The source of the nitrogen for MCR in these LNG refrigeration plants can be an air separation unit; methane is available from the gas feed. The feed gas to most LNG plants typically contains several percent each of ethane and propane which, as is known in the art, can be easily recovered via condensation and distillation for use as refrigerant components. Some natural gases, however, are very lean, containing such small amounts of ethane or propane that no preferential condensation occurs before the main exchanger used in the LNG refrigerant process. LNG plants processing such lean gases presently must import the ethane (or ethylene) and propane required to meet the MCR refrigerant needs. Since LNG plants are typically located remote from other hydrocarbon processing plants, importing these ethane (or ethylene) and propane refrigerants can be a costly and complicated matter.